Biological filter and process

Abstract

A biological filter apparatus, and process for using the same, wherein organic pollutants in a waste water stream may be biologically degraded by a biomass of suitable microorganisms located on the surface of a packing. The filter comprises a sealed vessel in which the packing having the biomass thereon is located, and the waste water, mixed with several volumes of liquid recycle, is allowed to trickle downwardly through the packing countercurrently to ascending gases, effluent liquid is removed from the bottom of the vessel at a rate sufficient to maintain the level of effluent liquid below the packing in order to prevent the packing from being submerged in liquid. The apparatus and process are applicable to the anaerobic methanogenic processes wherein methane is produced as a product; and are also applicable to non-methanogenic processes which are conducted in the absence of added molecular oxygen wherein combined nitrogen is converted to molecular nitrogen. Extrinsic gases may be added to the filter at a point below the packing to aid in the degradation.

The embodiments of the invention in which an exclusive right or privilege is claimed are defined as follows: 
     
       1. A continuous biological degradation process wherein a liquid waste water stream containing organic pollutants amenable to biological degradation is contacted with a biomass of microorganisms located on the surface of a support packing so as to effect the biological degradation of said organic pollutants to carbon dioxide and other products, said microorganisms being capable of degrading said organic pollutants to carbon dioxide and other products, said process being conducted in the absence of added molecular oxygen, which process comprises: (a) continuously passing a liquid mixture comprised of said waste water stream and the hereafter defined recycle stream downwardly through a packed section confined within a sealed vessel, said packed section being filled with the said support packing on the surface of which is a said biomass of said microorganisms, said sealed vessel being sealed whereby air and other sources of molecular oxygen cannot enter said sealed vessel, such that said liquid mixture intimately contacts said biomass as its descends through said packed section under conditions whereby at least a portion of the organic pollutants from said waste water stream are biologically degraded and converted to carbon dioxide and other products and resulting in a liquid effluent from the lower end of said packed section containing a lower concentration of said organic pollutants than in said liquid mixture, and whereby liquid descends through said packed section while carbon dioxide and other gases generated in the biological degradation ascend through said packed section countercurrently to the descending liquid, the contacting of said liquid mixture with said biomass being accomplished at a temperature within the range of about 10° to 60° C. which is suitable for said biological degradation and at substantially atmospheric pressure;   (b) continuously withdrawing from the upper end of said sealed vessel at a point above said packed section the said carbon dioxide and other gases generated in the said biological degradation;   (c) continuously withdrawing said liquid effluent from the lower end of said sealed vessel at a point below said packed section, the rate of withdrawal of said liquid effluent being such as to maintain the liquid level of any said liquid effluent accumulating in the bottom of said sealed vessel below said packed section, a portion of said liquid effluent being withdrawn as a treated waste water outfall stream; and   (d) continuously recycling as a said recycle stream a portion of said liquid effluent withdrawn from the lower end of said sealed vessel and mixing said recycle stream with said waste water stream prior to passing the resulting said liquid mixture downwardly through said packed section in accordance with the preceding step (a), the portion of said liquid effluent so recycled as said recycle stream being at least 60% thereof and an amount that, when mixed with said waste water stream, will cause the said liquid mixture to have a concentration of said organic pollutants and of any biostatic or biocidal species to be below that concentration which would inhibit the growth processes of said microorganisms.   
     
     
       2. The process of claim 1 wherein the said liquid mixture passed downwardly through said packed section is buffered to a pH that would not inhibit the growth processes of said microorganisms and would not kill the said microorganisms. 
     
     
       3. The process of claim 2 wherein the weight ratio of said recycle stream to said waste water stream is within the range of about 5:1 to 100:1, and wherein the C.O.D. of the resulting said liquid mixture is within the range of about 500 to 20,000 milligrams per liter. 
     
     
       4. The process of claim 3 wherein the void volume of said packed section is at least about 60% of the unpacked volume of said packed section, wherein the surface area of packing in said packed section is at least 10 square feet per cubic foot, and wherein the said liquid mixture is passed to said packed section at a rate to provide a C.O.D. loading within the range of about 0.2 to 4.0 C.O.D. per cubic foot of void volume of said packed section per day, and to provide from about 0.1 to 10 volumes of said liquid mixture per void volume of said packed section per day. 
     
     
       5. The process of claim 4 wherein said organic pollutants are water soluble. 
     
     
       6. The process of claim 1 wherein said organic pollutants are water soluble. 
     
     
       7. The process of claim 1 wherein said waste water stream contains heavy metals toxic to said biomass, and wherein a sulfur compound is added to react with and precipitate the heavy metals as insoluble sulfides. 
     
     
       8. The process of claim 7 wherein said sulfur compound is gaseous hydrogen sulfide which is added in the form of a gas to said sealed vessel at a point below said packed section whereby said hydrogen sulfide ascends through said packed section countercurrently to and in intimate contact with the descending liquid. 
     
     
       9. A continuous methanogenic, anaerobic biological degradation process wherein denitrification is not accomplished and wherein a liquid waste water stream containing organic pollutants amenable to biological degradation is contacted with a biomass of anaerobic microorganisms located on the surface of a support packing so as to effect the biological degradation of said organic pollutants to carbon dioxide, methane and other products, said microorganisms being capable of degrading said organic pollutants to carbon dioxide, methane and other products, said process being conducted in the absence of molecular oxygen, which process comprises: (a) continuously passing a liquid mixture comprised of said waste water stream and the hereafter defined recycle stream downwardly through a packed section confined within a sealed vessel, said packed section being filled with the said support packing on the surface of which is a said biomass of said microorganisms, said sealed vessel being sealed whereby air and other sources of molecular oxygen cannot enter said sealed vessel, such that said liquid mixture intimately contacts said biomass as it descends through said packed section under conditions whereby at least a portion of the organic pollutants from said waste water stream are biologically degraded and converted to carbon dioxide, methane, and other products and resulting in a liquid effluent from the lower end of said packed section containing a lower concentration of said organic pollutants than in said liquid mixture, and whereby liquid descends through said packed section while carbon dioxide, methane and other gases generated in the biological degradation ascend through said packed section countercurrently to the descending liquid, the contacting of said liquid mixture with said biomass being accomplished at a temperature within the range of about 10° to 60° C. which is suitable for said biological degradation and at substantially atmospheric pressure;   (b) continuously withdrawing from the upper end of said sealed vessel at a point above said packed section the said carbon dioxide, methane and other gases generated in the said biological degradation;   (c) continuously withdrawing said liquid effluent from the lower end of said sealed vessel at a point below said packed section, the rate of withdrawal of said liquid effluent being such as to maintain the liquid level of any said liquid effluent accumulating in the bottom of said sealed vessel below said packed section, a portion of said liquid effluent being withdrawn as a treated waste water outfall stream; and   (d) continuously recycling as a said recycle stream a portion of said liquid effluent withdrawn from the lower end of said sealed vessel and mixing said recycle stream with said waste water stream prior to passing the resulting said liquid mixture downwardly through said packed section in accordance with the preceding step (a), the portion of said liquid effluent so recycled as said recycle stream being at least 60% thereof and an amount that, when mixed with said waste water stream, will cause the said liquid mixture to have a concentration of said organic pollutants and of any biostatic or biocidal species to be below that concentration which would inhibit the growth processes of said microorganisms.   
     
     
       10. The process of claim 9 wherein the said liquid mixture passed downwardly through said packed section is buffered to a pH that would not inhibit the growth processes of said microorganisms and would not kill the said microorganisms. 
     
     
       11. The process of claim 10 wherein the weight ratio of said recycle stream to said waste water stream is within the range of about 5:1 to 100:1, and wherein the C.O.D. of the resulting said liquid mixture is within the range of about 500 to 20,000 milligrams per liter. 
     
     
       12. The process of claim 11 wherein the void volume of said packed section is at least about 60% of the unpacked volume of said packed section, wherein the surface area of packing in said packed section is at least 10 square feet per cubic foot, and wherein the said liquid mixture is passed to said packed section at a rate to provide a C.O.D. loading within the range of about 0.2 to 4.0 C.O.D. per cubic foot of void volume of said packed section per day, and to provide from about 0.1 to 10 volumes of said liquid mixture per void volume of said packed section per day. 
     
     
       13. The process of claim 12 wherein said organic pollutants are water soluble. 
     
     
       14. The process of claim 12 wherein a gas comprising hydrogen is passed to said sealed vessel at a point below said packed section whereby said hydrogen ascends through said packed section countercurrently to and in intimate contact with the descending liquid, the amount of said gas being passed to said sealed vessel being such as to provide not greater than about 3.5 moles of hydrogen per mole of carbon dioxide being formed in said biological degradation. 
     
     
       15. The process of claim 14 wherein said organic pollutants are water soluble. 
     
     
       16. The process of claim 9 wherein said organic pollutants are water soluble. 
     
     
       17. The process of claim 9 wherein said waste water stream contains heavy metals toxic to said biomass, and wherein a sulfur compound is added to react with and precipitate the heavy metals as insoluble sulfides. 
     
     
       18. The process of claim 17 wherein said sulfur compound is gaseous hydrogen sulfide which is added in the form of a gas to said sealed vessel at a point below said packed section whereby said hydrogen sulfide ascends through said packed section countercurrently to and in intimate contact with the descending liquid. 
     
     
       19. The process of claim 9 wherein a gas comprising hydrogen is passed to said sealed vessel at a point below said packed section whereby said hydrogen ascends through said packed section countercurrently to and in intimate contact with the descending liquid, the amount of said gas being passed to said sealed vessel being such as to provide not greater than about 3.8 moles of hydrogen per mole of carbon dioxide being formed in said biological degradation. 
     
     
       20. A continuous biological degradation process wherein a liquid waste water stream containing organic pollutants amenable to biological degradation, and also containing nitrogen compounds wherein combined nitrogen is present as a nitrate, a nitrite or a nitrogen oxide, is contacted with a biomass of microorganisms located on the surface of a support packing so as to effect the biological degradation or conversion of said organic pollutants to carbon dioxide and other products, and to effect the biological degradation or conversion of said combined nitrogen to molecular nitrogen, said microorganisms being capable of degrading said organic pollutants to carbon dioxide and other products and of degrading or converting said combined nitrogen to molecular nitrogen, said process being conducted in the absence of added molecular oxygen, which process comprises: (a) continuously passing a liquid mixture comprised of said waste water stream and the hereafter defined recycle stream downwardly through a packed section confined within a sealed vessel, said packed section being filled with the said support packing on the surface of which is a said biomass of said microorganisms, said sealed vessel being sealed whereby air and other sources of molecular oxygen cannot enter said sealed vessel, such that said liquid mixture intimately contacts said biomass as it descends through said packed section under conditions whereby at least a portion of the organic pollutants from said waste water stream are biologically degraded and converted to carbon dioxide and other products and at least a portion of the combined nitrogen from said waste water stream is converted to molecular nitrogen and resulting in a liquid effluent from the lower end of said packed section containing a lower concentration of said organic pollutants and a lower concentration of said nitrogen compounds than in said liquid mixture, and whereby liquid descends through said packed section while carbon dioxide, molecular nitrogen and other gases generated in the biological degradation ascend through said packed section countercurrently to the descending liquid, the contacting of said liquid mixture with said biomass being accomplished at a temperature within the range of about 10° to 60° C. which is suitable for said biological degradation and at substantially atmospheric pressure;   (b) continuously withdrawing from the upper end of said sealed vessel at a point above said packed section the said carbon dioxide, molecular nitrogen and other gases generated in the said biological degradation;   (c) continuously withdrawing said liquid effluent from the lower end of said sealed vessel at a point below said packed section, the rate of withdrawal of said liquid effluent being such as to maintain the liquid level of any said liquid effluent accumulating in the bottom of said sealed vessel below said packed section, a portion of said liquid effluent being withdrawn as a treated waste water outfall stream; and   (d) continuously recycling as a said recycle stream a portion of said liquid effluent withdrawn from the lower end of said sealed vessel and mixing said recycle stream with said waste water stream prior to passing the resulting said liquid mixture downwardly through said packed section in accordance with the preceding step (a), the portion of said liquid effluent so recycled as said recycle stream being at least 60% thereof and an amount that, when mixed with said waste water stream, will cause the said liquid mixture to have a concentration of said organic pollutants, and of any said nitrogen compounds, and of any biostatic or biocidal species to be below that concentration which would inhibit the growth processes of said microorganisms.   
     
     
       21. The process of claim 20 wherein the said liquid mixture passed downwardly through said packed section is buffered to a pH that would not inhibit the growth processes of said microorganisms and would not kill the said microorganisms. 
     
     
       22. The process of claim 21 wherein the weight ratio of said recycle stream to said waste water stream is within the range of about 5:1 to 100:1, and wherein the C.O.D. of the resulting said liquid mixture is within the range of about 500 to 20,000 milligrams per liter. 
     
     
       23. The process of claim 22 wherein the void volume of said packed section is at least about 60% of the unpacked volume of said packed section, wherein the surface area of packing in said packed section is at least 10 square feet per cubic foot, and wherein the said liquid mixture is passed to said packed section at a rate to provide a C.O.D. loading within the range of about 0.2 to 4.0 C.O.D. per cubic foot of void volume of said packed section per day, and to provide from about 0.1 to 10 volumes of said liquid mixture per void volume of said packed section per day. 
     
     
       24. The process of claim 23 wherein said organic pollutants are water soluble. 
     
     
       25. The process of claim 23 wherein a gas comprising one or more nitrogen oxides is passed to said sealed vessel at a point below said packed section whereby said nitrogen oxides ascend through said packed section countercurrently to and in intimate contact with the said descending liquid. 
     
     
       26. The process of claim 23 wherein said organic pollutants are water soluble. 
     
     
       27. The process of claim 20 wherein said organic pollutants are water soluble. 
     
     
       28. The process of claim 20 wherein said waste water stream contains heavy metals toxic to said biomass, and wherein a sulfur compound is added to react with and precipitate the heavy metals as insoluble sulfides. 
     
     
       29. The process of claim 28 wherein said sulfur compound is gaseous hydrogen sulfide which is added in the form of a gas to said sealed vessel at a point below said packed section whereby said hydrogen sulfide ascends through said packed section countercurrently to and in intimate contact with the descending liquid. 
     
     
       30. The process of claim 20 wherein a gas comprising one or more nitrogen oxides is passed to said sealed vessel at a point below said packed section whereby said nitrogen oxides ascend through said packed section countercurrently to and in intimate contact with the said descending liquid. 
     
     
       31. The process of claim 30 wherein said gas comprises nitrous oxide.